1. FIELD OF THE INVENTION
This invention relates to an objective lens driving device for use in an optical disk apparatus or the like.
2. PRIOR ART
An objective lens driving device is known in which an objective lens is mounted on a rocker arm in a relation spaced apart from a shaft supporting the rocker arm, and the rocker arm is provided which means for driving the objective lens in the axial direction of the supporting shaft (the focusing direction) and means for driving the objective lens in the rotating direction of the rocker arm (the tracking direction).
According to the known device, impartation of a driving force to one end of the rocker arm produced a large torque driving the objective lens in the tracking direction, so that the size of the driving means driving the objective lens in the tracking direction can be reduced. However, in this known device, the driving force imparted to the end of the rocker arm (the tracking arm) is not balanced with respect to the supporting shaft. As a result, the rocker arm is urged straight in the direction of the driving force by an amount corresponding to a very narrow gap between the supporting shaft and the cylindrical hole of the rocker arm through which the shaft extends. Thus, the resultant displacement of the objective lens is the sum of the rotating movement and the straightforward movement. When the frequency of the driving force imparted to the end of the rocker arm coincides with the resonance frequency of the supporting shaft, the cylindrical hole portion of the rocker arm collides against the supporting shaft at the resonance frequency of the supporting shaft to cause resonance of the supporting shaft. The resonance of the supporting shaft results in a large displacement of the objective lens in the straightforward moving direction, and this results in a great deviation of the amplitude and phase of the displacement of the objective lens in the tracking direction. Under such a situation, it is difficult to stably drive the objective lens in the tracking direction.